This isn't exactly a tip or trick, and I don't remember if this has been posted before, but even if it has, maybe it's time to say it again anyway.
Yesterday I went to work on one of my machines, but started running into problems with HD space right away. I ran
df and it showed my normally 15GB /home partition had filled up to the entire 70GB alloted!
I hadn't looked for a good disk usage analyzer in GUI version for some time, and after a (very) brief Synaptic search, I logged into my Gnome DE and used Disk Usage Analyzer (nice name

- see last paragraph), an excellent tool for the purpose of tracking down specific folder overloads. It immediately became clear that the hidden ./dropbox folder was the culprit. When I saw that, I remembered recently uploading a video file to Dropbox on another computer, and when I opened the folder, sure enough, Dropbox was uploading it over and over again.
Why? Well,
I had used a non-standard directory on a USB drive as my Dropbox folder. Not a good idea, obviously - when Dropbox lost track of that drive for whatever reason, it tried to download the same 175MB file over and over and over in the only "dropbox" folder it could find...
I do remember that JohnBoy/Just19 told me about a KDE tool long ago that is similar to Disk Usage Analyzer, but hey, I'm old and can't remember anything more than one day. In any case, I found that the real name of Disk Usage Analyzer is
baobab and it runs nicely in KDE from the cli. In fact I like it so much that I added it to my menu.
BTW, if you want a good laugh out of all this, try searching Synaptic using
disk usage analyzer!
